SYNTAX ZX80 Vol. 2 No. 6

SYNTAX ZX80

A PUBLICATION OF THE HARVARD GROUP

VOL. 2 NO. 6 ISSN 0273-2696 JUN., 1981

CAI UPDATE

CAI Ins tr laments is almost
ready with their Widget series
peripherals for ZX80s and
MicroAces. One small problem
remains. The Widget series tape
drive, printer and Widget board
were compatible with the original
Sinclair 8K ROM. Like most of us,
CAI has only just gotten their new
8K ROM and now must check that
their peripherals do not interfere
with the functions of the new ROM.
According to Bob Swann of CAI,
this should delay production only
about two weeks. Swann also
announced that CAI is developing
home financial software to keep
budget and income tax records.
Prices are not definite, but they
should come in under $20. Some
programs will be ready in June.

NEWS FROM MICROACE

MicroAce and ZX80 owners who
want the flicker- free feature of
the ZX81 can get it with an add-on
board from MicroAce. The board
contains only 6-7 chips and
solders onto your PC board. The
cover fits over the machine with
the board installed, although the
fit is a little tight on a ZX80.
According to Chris Cary of
MicroAce, the add-on board will
cost $29.50 and be available by
June. Contact MicroAce at 1348 E.
Edinger, Santa Ana, CA, 92705,
714/547-2526.

MicroAce' s Santa Ana shop
will expand to sell other personal
computer brands, including the
PMC, VIC-20, PET, and TRS-80 Color
Computer.

MICROPERIPHERAL ABANDONS MODEM

Microperipheral Corp. of
Mercer Island, WA, has given up
its plans to produce ZX80 modems,
according to Lucy Stoner of Micro-
peripheral. Because they had to
add many hardware features not in
the ZX80, she said, the modem
would have cost more than the
original computer.

EZUG NEWSLETTER

The Educational ZX80/1 Users'
Group (EZUG) publishes a news-
letter each month for ZX80 users.
The British EZUG newletter covers
programs and ideas from its
membership for educational uses of
the ZX80 and ZX81 computers. Just
send a self-addressed stamped
envelope for delivery. (The copy
we saw would cost 40$ for airmail
postage.) SYNTAX has arranged an
information exchange with Eric
Dees on, organizer of EZUG, to
bring you ideas from overseas.

For more information, contact Eric
at Highgate School, Balsall Heath
Rd. , Birmingham, England, B12 9DS.

The 8K ROM produces a different
screen display than the 4K ROM.
SYNTAX will publish listings in 4K
format, but we will print both 4K
and 8K Syntactic Sums for programs
that run in either machine.

Rochester Institute of Technology
offers two intensive computer
courses for deaf adults in Augus t .
Contact Donald Beil, NTID Data
Processing Dept. , RIT, 1 Lomb
Memorial Dr. , Rochester, NY,

14623, 716/475-6373, voice or TTY.

1

SYNTAX ERRORS

May 81 — Marty Iron's Line
Renumbering program contained an
error. Line 9130 should read:

9130 IF PEEK(S)=*248 THEN GO TO
9300.

Our list of new 8K ROM features
should have included the INT (X)
function.

4K PROGRAMS ON 8K ROM

By now you know your 8K ROM
won ' t load 4K tapes . So far , all
you can do is retype the program.

Why so? The 8K system looks
for file headers, or leading name
fields (you must name files), even
using LOAD "" (load first program
f ound) . A 4K tape lacks headers ,
so the 8K system can't tell where
4K programs begin. If you loaded
a 4K program, your 8K ROM would
read it using the wrong character
codes. For example, code 18 means
minus to 4K ROMs and greater than
to the 8Ks. And the keyword codes
also changed. Your 8K tapes hold
programs and system variables; 4K
tapes won't set these properly.

Even if you overcome these
difficulties, you'll find your old
programs don' t run if they depend
on integer arithmetic, logic true
being -1, the TL$ function, or the
masking properties of the 4K ROM's
logical functions.

Is the situation hopeless?
Only until someone works out how
to program the translation between
notations. The 4K and 8K BASIC
are nearly compatible. A routine
diverting LIST to a 4K machine bus
via a translation table may, with
interfacing, send 4K programs to
the bus of a second 8K machine in
8K codes. Of course, this plan
needs 2 ZX80s.

Or perhaps someone can invent
a program for 4K machines to write
simulated 8K tapes. Or a program
to read a 4K tape on 8K machines.

We'll publish solutions as we
learn of them.

BEGINNERS' COMPUTING MAGAZINE

OnComputing , a quarterly
computer magazine, is going
monthly and changing its name to
Popular Computing. The new
magazine will be for "intelligent
readers who lack a technical
background" and will be edited
exclusively for beginners.

Chris topher Morgan , founding
editor of onComputing and editor-
in-chief of BYTE, will remain as
editor of Popular Computing.
Contact onComputing, Inc. , 70 Main
St. , Peterborough, NH, 03458.

OUR POLICY ON CONTRIBUTED MATERIAL

SYNTAX ZX80 invites you to express opinions related to the ZX80 and the
newsletter. We will print, as space allows, letters discussing items of general interest.

Of course, we reserve the right to edit letters to a suitable length and to refuse
publication of any material.

We welcome program listings for all levels of expertise. Programs can be for
any fun or useful purpose. We will test run each one before publishing it, but we
will not debug programs; please send only workable listings.

In return for your listing, we will pay you a token fee of $2.00 per program we
use. This payment gives us the nonexclusive right to use that program in any fora,
world-wide. This means you can still use it, sell it, or give it away, and so can we.

We will consider submissions of news and hardware or software reviews. Pteme
keep articles short (350-400 words). Again, we reserve the right to edit accepted
articles to a suitable length. We will pay 7 cents per 6 characters, including s pa ces
and punctuation, for accepted articles.

When you send in programs for possible publication in SYNTAX, pleax
include the following information:

• How to operate the program, including what to input if it does not
prompts.

• Whether you can run the program over again and how.

• How to exit the program.

• The Syntactic Sum (using the Syntactic Sum program in the February, 1981,
issue).

• Whether it Fits in IK or 2K RAM (or 16K when available).

• Whether it uses the 4K or 8K RAM.

We pay for this explanatory text at the same rate as for articles in addition to
payment for the program itself.

If you want us to return you original program listing or article, please include a
self-addressed, stamped envelope. Otherwise, we cannot return submitted material.

SYNTAX ZX80 is published monthly

by Syntax ZX80, Inc., a wholly-owned subsidiary of

The Harvard Group, RD 2, Box 457, Bolton Road,

Harvard, MA 01451. Telephone 617/456-3661.

Subscriptions: 12 issues, $25. Single issue, $4.

Publisher: Kirtland H. Olson
Editor: Ann L. Zevnik
Associate Editor: Susan G. Barber

Technical consultant: Eric K. Olson

Printed by Joseph E. Marhefka, Jr.

Clinton Offset Printers
Clinton, MA 01510

© Syntax ZX80, Inc., 1981. All rights reserved.

Photocopying prohibited. ISSN 0273-2696

2

INVERSE CRYPTOLOGY

This challenging code break-
ing game for 2 uses 4K ROM and IK
RAM. The computer encodes the
secret phrase typed in by player
1. Player 2 guesses by typing
letter=letter. A correct guess
replaces the coded letter with the
correct inverse letter.

DIM (25) stores the code.
Subscripts 0 to 25 represent the
real alphabet. The program
recodes the phrase each time it
prints it instead of storing a
separate coded phrase. It's
slower but uses less memory.

Enter up to 1 line. To use
up to 84 characters, delete line
425 and change line 410 to PRINT
"ENTER LETTER=LETTER" . To exit,
break the code or hit SHIFT BREAK
quickly after a guess. To play
again, hit RUN twice, then (NL) .

Harold A. Lamkin, Mt. Clemens, MI

10 DIM A(25)

20 RANDOMISE
30 FOR Z=0 TO 25
40 LET A (Z) =RND (26) +37
60 FOR X=0 TO 25
70 IF A(Z)=A(X) AND NOT Z=X TH
EN GO TO 40
80 NEXT X
90 NEXT Z

100 PRINT "STATE A PHRASE"

110 INPUT W$

120 GO SUB 600
400 PRINT

410 PRINT "ENTER PHRASE OR LETT
ER= LETTER"

420 INPUT U$

425 IF U$=W$ THEN GO TO 900
430 IF NOT CODE (TL$ (U$) ) =227 TH
EN GO TO 700

440 LET Y=CODE (TL$ (TL$ (U$) ) )

450 IF Y<38 OR Y>63 THEN GO TO
700

460 IF NOT A ( Y- 3 8 ) =CODE (U$) THE
N GO TO 700
470 LET A(Y-38)=Y+128
480 CLS

485 PRINT "CORRECT"

490 GO SUB 600

491 IF Z— 0 THEN GO TO 900

495 GO TO 400

600 PRINT

605 LET Z=0

610 LET U$=W$

620 LET Y=CODE(U$)

630 IF Y<38 OR Y>63 THEN PRINT
CHR$ (Y) g

640 IFY<38 OR Y>63 THEN GO TO
650

645 PRINT CHR$ (A(Y-38) ) ;

646 IF NOT A(Y-38)=Y+128 THEN L
ET Z=Z+1

650 IF Y=1 THEN GO TO 680
660 LET U$=TL$(U$)

670 GO TO 620
680 PRINT
690 RETURN
700 LET X=X+1
705 CLS

710 PRINT "TRY AGAIN"

720 GO SUB 600
730 GO TO 400
900 CLS

910 PRINT "YOU BROKE THE CODE W
ITH ";X-26;" ERRORS "?W$
Syntactic Sum=-71 9 1

NOW AVAILABLE

keyboard .

x Conversions

• Standard Computer Keyboard

• Type programs in half the time

• Minimize errors

• Wired keyboard hooks up in minutes

Plans for keyboard conversion with reverse video
$10.00

Keyboard with complete parts and plans $65.00
Wired keyboard, complete with plans $85.00

Mail for information:

L. J. H. Enterprises

P.O. Box 6273, Orange, CA 92667

3

ALL-PURPOSE BEEPER

Here's a nifty circuit to
emit a "beep" every time your ZX80
or MicroAce reads from or writes
to a selected memory address.

Four comparators, the heart of the
circuit, constantly compare the
address on the bus to the address
set on a bank of 16 switches.

When the two are equal, a 555
timer is started, which runs
another 555 oscillator. The tiny
switches in the circuit must be

To get a beep when

set in binary, one digit at a
time. The switch which would be
used for A15 is left always
grounded instead and compared to
NOT MREQ. The schematic this page
shows how to construct this
circuit. Use a 2 inch 10 ohm
speaker to emit the beep.

Now you can hear every time
the computer executes a certain
byte of code. Depending on what
you set the switches to, you can
hear the beep for nearly any
occurence within your computer.

Set switches, as

Newline key pressed 0283
Keystroke ignored (NL with error, etc.) 03A7
Keystroke results in syntax error 08AE
Character printed on the screen 4024
Printing on screen advances to a new line 4025
Rubout pressed 0395
Screen is cleared (By any method) 0747

Keystrokes in line beginning with illegal keyword 07BB

4

MACHINE LANGUAGE PROGRAMMING-
MULTIPLICATION AND DIVISION

Last time we tried Sinclair's
machine language (ML) routine for
determining available memory. It
added 11 to the stack pointer and
returned an answer to BASIC — easy
stuff. Subtraction in binary is
also easy; sub tract column-by-
column and borrow when necessary.

Multiplication and division
require more thought and attention
to detail. One or two commands
will not multiply 2 numbers, as in
BASIC. Still, ML multiplication
and division routines are
straightforward. If you don't
understand some terms here, don't
worry — just follow the logic and
use the program as a recipe.

Refer to the books by Rodnay

Zaks (Programming tha ZftQ , 2d ed.
pp. 113-136) and Kathe Spracklen
(Z-80 and 8080 Assembly Language
Programming r pp. 60-65) for more
details. Zaks shows sample code
and Spracklen gives math examples.

Glance through this assembly
listing that converts degrees
Fahrenheit to Celsius using the
formula C ss 5(F-32)/9. (This problem
would be easier to solve using
BASIC, but we'll use ML to see how
it's done). The first column is
the memory address where beginning
bytes of instructions reside. If
the instruction needs more bytes,
they will be stored in successive
locations. The second column
lists hexadecimal program codes
(you can enter these using Matthew
Johnson's Hex Monitor, May 81).
Column three labels subroutines--

CHEST or CMSSICS

FOUR CLASSIC COMPUTER GAMES
FOR THE ZX80 AND MICRO ACE.

LUNAR LANDER
MINDMASTER

K-TREK

LIFE

PLAY LIFE, A MACHINE -LANGUAGE ROUTINE LETS YOU GROW 1000 GENERATIONS /MINUTE.
PLAY K-TREK, THE STAR TREK GAME IN IK.

PLAY MINDMASTER, A GRAPHIC VERSION OF MASTERMIND,

WITH 9 LEVELS OF DIFFICULTY.

ALL FOUR GAMES ON ONE CASSETTE, WITH
GAME MANUAL, CHARTS, COLOR KEYBOARD
OVERLAYS, COMPLETE LISTING IN BASIC,

AND MOREI

JUST POP IN THE CASSETTE AND PLAY I
(REQUIRES 4K BASIC & IK MEMORY OR MORE).

ALSO: OLD *1

FAMILIAR OLD PROGRAMS LIKE DICE THROW,
MULTIPLICATION TABLES, AND ALSO MANY NEW,
LIKE AUTO-PLOT (GRAPHS YOUR EQUATIONS,
COMPLETE WITH LABELED AXES). ELECTRIC
NOTEPAD LETS YOU CREATE PHONE LISTS, ETC..
GAMES, PUZZLES, TEN PROGRAMS IN ALL.

ALL ON ONE CASSETTE, YOUR CHANCE TO
TRY OUR SOFTWARE. JUST $2,991

$ 9- 95

NO POSTAGE.
NO HANDLING.
NO SALES TAX.

FREE!

WRITE FOR OGR
FREE CATALOG &
RECEIVE ZX80 &
MICROACE CODING
SHEETS.

LAMO-LEM LABS

LA JOLLA

5

marking parts of the program.
Assembly language commands are in
the fourth and fifth columns . The
last column contains comments,
preceded by semicolons. Like REM
statements, comments identify
functions of the lines.

Note the repetitive look of
commands in column five. Good ML
programming breaks problems into
small tasks the computer can do.

In decimal multiplication,
you shift each partial product 1
column to the left for each left
shift you make in the multiplier:

(multiplicand) 32

(multiplier) x 15

(partial product) 160

(partial product) 32

(product) 480

Mentally, you do 1x32, and shift 1
place left to multiply by 10.

Look closely and you'll see
the routine shifts the multiplier
in register C to the right. Shift
either way, but stick to one
direction throughout the problem,
as iii this decimal example:

SHIFT LEFT

SHIFT RIGHT

23

23

x 12

x 12

46

23

23

46

276

276

In binary multiplication all
partial products are either the
multiplicand or a row of zeros,
since 1 times any number is that
number and 0 times any number is
0. (Examine the multiplication,
and remember, 1+1= 10 in binary.
Carry the 1 to the next column, as
in decimal addition.)

At the end of SUBT (sub-
tract) , we have taken the Fahren-
heit value from a POKEd memory
address (see PEEK-POKE story this
issue), subtracted 32, and left
the multiplicand (F-32) in the E
half of the DE register pair, a
temporary Z80 storage location.

MULMR loads the multiplier
(5) and sets a bit-counter in
register B (again, a temporary
storage location) that we count

down with each shift. Z80's use a
special command, DJNZ PROCESS,
that decrements B and jumps to the
named process if B is not 0. When
B is 0, the Z80 knows it's done.

MULT multiplies binary
numbers bit-by-bit, as you multi-
ply decimal numbers column-by-
column. MULT shifts the multiplier
right into the carry bit and adds
the result to the HL register each
time the carry bit is 1. The loop
continues until the bit- counter
reads 0 (at the other end of the
multiplier) meaning all bits have
been counted. Meanwhile, the HL
register pair accumulates a
running partial product total.
C-register ^carry bit
11001101 0 (beginning)
0>01100110 1 (incr prod & shift)
0>00 110011 0 (shift only)

Dividing is like multiplying,
except that the divisor (number
you divide by) is subtracted from
the dividend (number you divide
into) . DIV performs binary long
division after DIV66 loads the
divisor (9) into D, zeros E and
resets the bit-counter, B. Each
time the computer subtracts divi-
sor from dividend, it adds 1 to
the quotient and shifts the new
dividend and quotient left 1 bit.

The following examples show
how long division is the same in
both decimal and binary:

DECIMAL

103

2112163

2lU

063

quotient
divisor I dividend

BINARY

1100111

101011 100001110011
10 10 1 1
11001
10 101 1 Ji
100100
lOlOll
11111
lOlOll

ent 10101

end 10101

0

If the subtraction yields a
negative result, the program must
restore the quotient total and the

6

dividend to their previous values
prior to proceeding. Finally the
answer is in L and the remainder
in H; the next- to- last command
zeros the remainder.

This routine returns integer
quotients to BASIC. Use C9 as the
last command to get back to BASIC
from machine language .

You can convert Fahrenheit
values from 32 to 491 degrees.
Beyond these limits, the program
fails because the result in the L
register is outside its 0-255° C
range. Another program must handle
negative or larger results.

To run the program, you need
to POKE a Fahrenheit value from
BASIC. For 32-255° F, POKE 17357,
val of F and POKE 17358,0. For
256-491 F, POKE 17357, val of F-256

ASSEMBLY LISTING (4K only; see p.12)

and POKE 17358,1. After POKEing
the values, use PRINT USR(17359)
to see the result.

You can write a whole BASIC
program to use this ML program.
First, enter the memory protect
program, p.8. Use 1 for K and 51
for N. This saves 51 bytes at the
top of memory from encroachment
from BASIC programs. DO NOT TYPE
NEW ON 4K ROMS. Load Hex Monitor
and change the starting address to
be 17407 (top of IK RAM) minus the
bytes you reserved, 51, in line
90. Input the hex values for the
conversion program. Then load or
type in a BASIC program to. ask for
Fahrenheit values, POKE the ML
memory locations, call the USR
routine at 17407-51+2 (to avoid
the 2 bytes where you POKEd in the
F values) and display the results.

43CD

00080

ORG

43CDH

43CD

0000

00090 TEMP

DEFW

0

43CF

2ACD43

00100 SUBT

LD

HL, (TEMP)

LOAD FAHREN

43D2

1600

00110

LD

D,0

CLEAR D

43D4

1E20

00120

LD

E,20H

LOAD SUBTRAHEND

43D6

A7

00130

AND

A

CLEAR CARRY

43D7

ED52

00140

SBC

HL,DE

FAHRENH-32

43D9

EB

00150

EX

DE,HL

RESULT INTO DE

43DA

210000

00160

LD

HL, 0

CLEAR HL

43DD

0E05

00170 MULMR

LD

C,5H

LOAD MULTIPLIER

43DF

0608

00180

LD

B,8H

INITIALIZE COUNTER

43E1

CB39

00190 MULT

SRL

C

SHFT RGT TO CARRY

43E3

3001

00200

JR

NC, NOADD

TEST CARRY

43E5

19

00210

ADD

HL,DE

(FAHRENH-32) +RESULT

43E6

EB

00220 NOADD

EX

DE,HL

43E7

29

00230

ADD

HL,HL .-DOUBLE SHIFT

43E8

EB

00240

EX

DE,HL

43E9

1 0F6

00250

DJNZ

MULT

LOOP UNTIL B=0

43EB

1609

00260 DIV66

LD

D,9H

LOAD DIVISOR

43ED

1E00

00270

LD

E,0

CLEAR E

43EF

0608

00280

LD

B,8H

INITIALIZE COUNTER

43F1

A7

00290 DIV

AND

A

CLEAR CARRY

43F2

ED52

00300

SBC

HL,DE

DIVID-DIVIS

43F4

23

00310

INC

HL

QUOT=QUOT+ 1

43F5

F2FA43

00320

JP

P , NOA2 2

TEST POSITIVE

43F8

19

00330

ADD

HL,DE

RESTORE IF NECESS

43F9

2B

00340

DEC

HL

QUOT=QUOT- 1

43FA

29

00350 NOA22

ADD

HL,HL

DOUBLE SHIFT

43FB

10F4

00360

DJNZ

DIV

LOOP UNTIL B=0

43FD

2600

00370

LD

H, 0

SET RMNDR ZERO

43FF

C9

00380

RET

7

PLACING USR CALLS IN 4K, 8K

Now that our readers use both
4K and 8K ROMs , SYNTAX supports
both sets of users. We'll tell
you how to overcome differences in
the 2 designs. Here's how to put
ML at the same addresses in both.

With the 8K ROM, USR routines
reside at high RAM addresses. You
POKE the first address you want to
use to locations 16388 & 16389
(p . 168 of ZX81 manual) . Use the
following program to get equal
space in 4K machines so SYNTAX ML
programs will run at specified
locations. Use of ROM routines
and system variables or locations
must change, but many routines
work in either machine.

Answer the first prompt with
the number of K of memory on your
machine. Respond to the second
prompt with the number of bytes
you want reserved. Next load your
BASIC program; it will be kept
away from the ML area. (The usual
program would aid loading ML, say

a monitor . )

Your first user location will
then be at 16382-N+(1024*K) .

5 INPUT K

6 INPUT N

7 LET M=16384+(K*1024)-1-N-1
10 POKE 17152,33

20 POKE 17153, M-CM/256)*256
30 POKE 17154, M/256
40 POKE 17155,195
50 POKE 17156,107
60 POKE 17157,2
70 LET X-USRC17152)

Syntactic Sump 11550, 4K

Although this program sets
aside space at the top of any size
memory, we will publish programs
assembled for IK memories. To use
our code directly, respond to the
first prompt with 1.

You input your memory size
and the space you want for USR
routines. This BASIC program then
loads HL with the address of a
fake top of RAM and jumps to the
INIT routine at 26BH, 619 dec (see
ROM listing) after the computer
would have set the memory top.

4K ROM LISTING — INITIALIZATION

0261 00070 ORG
40 0A 00071 E8LINE: EQU
4028 00072 RAMBOT: EQU
4008 00073 VARS: EQU
4000 00074 Y: EQU

In the 4K ROM listing below,
E8LINE means E-LINE.

026 1H roM contents © Sinclair Research

Ltd< Both Sinclair and SYNTAX
4U28H own copyright interests in this
400 8H material.

4000H

00075 ;INIT: ENTER HERE ON RESTART WITH HL= 7FFFH , A=3FH
0261 3601 00076 LI2: LD (HL) , 1 ;SET LOCS 4000H TO 7FFFH TO 1

0263 2B 00077 DEC HL

0264 BC 00078 CP H

0265 20FA 00079 JR NZ,LI2 ;LOOP UNTIL HL=3FFFH

0267 23 00080 LI3: INC HL ;SET ALL RAM LOCS TO ZERO

0268 35 00081 DEC (HL)

0269 28FC 00082 JR Z,LI3 ;LOOP UNTIL WRAPAROUND OR RUN OUT

026B F9 00083 LD SP,HL ; ASSUMES 1ST ROM BYTE IS NOT 01H

02 6C F5 00084 PUSH AF ;MARK "NO RETURN BLOCKS"

026D 3E0E 00085 LD A,0EH

026F ED47 00086 LD I, A

0271 ED56 00087 IM 1

0273 FD210040 00088 LD IY,Y

0277 212840 00089 LD HL, RAMBOT

027A 220840 00090 LD (VARS) ,HL;NO LINES OF PROGRAM

027D 3680 00091 LD (HL),80H ; VARIABLES CONSIST ONLY OF

02 7F 23 00092 INC HL ; TERMINATOR RECORD

0280 220A40 00093 LD (E8LINE) , HL ; LINE TO BE EDITED STARTS NEXT

8

ZX80 PRESTEL MODEL

This program is a model of
the British Prestel data base tree
structure. It can be used with
your own data for display to show
how Prestel data is accessed.

This version fits in IK; if you
have 16K and lots of patience, you
could create and record an impres-
sive dictionary in a given field.

From EZUG Newsletter, No, 3, pp.
7-8, Apr /May 81, Highgate School,
Balsall Heath Rd, Birmingham, B12
9DS, UK. Reprinted by permission.

(Note — Prestel is an on-line data
base retrieval system run by the
British Post Office. Meant for
the public, it uses phone lines
and home TV sets and resembles the
US Source network in theory. This
program is complete for choice 1.
Choices 2, 3, & 4 are only place
holders; they contain no data yet.
Try this format to create sequen-
tially accessed data, as in choice
1. Prestel doesn't fit in IK RAM
with 8K ROM, so we give no 8K
Syntactic Sum.)

10 LET A=0
20 GO SUB 5000

30 LET A$= "TYPE NUMBER NEEDED

II

40 PRINT A$

50 GO SUB 5100
60 PRINT "1. V, I, R"

70 PRINT "2. CIRCUIT EQUATION"

80 PRINT "3. POWER"

90 PRINT "4. RESISTORS"

100 GO SUB 5100

110 PRINT "OR TYPE 0 TO STOP"

120 INPUT B
130 CLS

140 IF B=0 THEN STOP
150 IF B<0 OR B>4 THEN GO TO 10
160 GO TO B*1000
1000 LET A=1
1010 GO SUB 5100
1020 PRINT A$

1030 GO SUB 5100

1040 PRINT "1. TO GET V"

1050 PRINT "2. TO GET I"

1060 PRINT "3. TO GET R"

1070 GO SUB 5100
1080 INPUT B
1090 CLS

1100 IF B<1 OR B>3 THEN GO TO 10
00

1110 GO TO 1 100+B*10Q
1200 LET A=1 1
1210 GO SUB 5000
1220 PRINT "USE V=IR"

1230 GO SUB 5200
1300 LET A=12
1310 GO SUB 5000
1320 PRINT "USE I=V/R"

1330 GO SUB 5200
1400 LET A=1 3
1410 GO SUB 5000
1420 PRINT "USE R=V/I "

1430 GO SUB 5200
2000 PRINT 2000
2010 GO SUB 5200
3000 PRINT 3000
3010 GO SUB 5200
4000 PRINT 4000
4990 STOP

5000 FOR C=2 TO 11
5010 PRINT " ";

5020 NEXT C

5030 PRINT "PAGE ";A

5040 GO SUB 5100

5050 RETURN

5100 FOR C=1 TO 3

5110 PRINT

5120 NEXT C

5130 RETURN

5200 GO SUB 5100

5210 PRINT "N/L TO RETURN TO IND
EX"

5220 INPUT C$

5230 CLS
5240 GO TO 10
5250 RETURN

Syntactic Sum=-16780,4K

PROGRAMMED RESPONSES— LATIN ROOTS

This program is a drill for
students of Latin and Greek. The
computer displays the Latin and
Greek root and the student types
in the correct English version.

Use this technique to write
your own programmed drills. Any
drill, like math or languages,
with predictable answers is suit-

9

able. Try adding lines to ask
student's name and use it during
the drill. Pete Cone's multipli-
cation program (Dec. 80) is a good
example. Or add PRINT statements
rewarding correct answers.

Daniel Ambrosini, Claverton, NY

10 PRINT "AG, AC",

15 INPUT A$

20 IF NOT A$=" DO" THEN GO TO 1

0

25 PRINT "AGR" ,

30 INPUT A$

35 IF NOT A$="FARM" THEN GO TO
25

40 PRINT "CAD, CAS",

45 INPUT A$

50 IF NOT A$="FALL" THEN GO TO
40

55 PRINT "CANT",

60 INPUT A$

65 IF NOT A$="SING" THEN GO TO
55

70 PRINT "CAP, CEP",

75 INPUT A$

80 IF NOT A$="TAKE" THEN GO TO
70

85 PRINT "CAPIT",

90 INPUT A$

95 IF NOT A$="HEAD" THEN GO TO
85

100 PRINT "CEDE",

105 INPUT A$

110 IF NOT A$="GO" THEN GO TO 1
00

115 PRINT "CELER",

120 INPUT A$

125 IF NOT A$=" SPEED" THEN GO T
0 115

130 PRINT " CLUD , CLUS " ,

135 INPUT A$

140 IF NOT A$=" CLOSE" THEN GO T
O 130

145 PRINT "CUR",

150 INPUT A$

155 IF NOT A$="RUN" THEN GO TO
145

160 PRINT "DICT",

165 INPUT A$

170 IF NOT A$="SAY" THEN GO TO
160

999 PRINT "END"

Syntactic Sum=-30558,4K 34142,8K

HARDWARE REVIEW: KEYBOARD BEEPER

Burnett Electronics' keyboard
beeper consists of a tiny piezo-
electric disk attached to two
integrated circuit chips on a
little circuit board. After
installation, the disk emits a
soft beep whenever you depress a
key. The entire apparatus fits
inside a ZX80 or MicroAce case.

All you need to wire the
circuit into your computer is a
soldering iron and the ability to
connect 12 wires. The circuit is
already internally wired. As the
rankest of beginners in electronic
circuit building, I was elected to
test the device and its written
directions. I successfully
installed my beeper the first time
in 20 minutes with no trouble.
Burnett's directions are
exceptionally clear and easy to
follow, even if you don't know a
resistor from a diode.

However, the installation
instructions did cause me two
slight problems: first, one wire
was tough to distinguish because
the directions identified it only
by color, and it looked just like
the other white wire nearby.
Second, my electronics experts had
to tell me to tape over the solder
side of the beeper circuit board
before taping it to my ZX80 case
to avoid shorting it, a precaution
Burnett did not mention. (This
does not matter with an unshielded
MicroAce, which has no
metallization inside the case.)

The circuit works perfectly
and produces variable tones as
long as you hold the key down.

The computer case gives it enough
resonance to make the sound loud
enough to hear but not be
annoying. If you have trouble
telling when you make contact with
the keys, this beeper can help you
type more quickly and accurately.
Keyboard beeper, $12.00, Burnett
Electronics, 908 Morris St. ,
Cincinnati, OH, 45206.

DEAR EDITOR:

In your article on new 8K ROM
features, several, such as READ-
DATA- RESTORE, LEFT$ , RIGHT$ , MID$,
DRAW- UNDRAW, INT(X) , were not on
your list. What happened to these
very important functions? Did you
forget to put them on your list?
Has Sinclair phased them out?

David Shulman, Peabody, MA

In redesigning the 8K ROM for
their printer, Sinclair eliminated
several planned features,
including most of those you
mention. LEFT$ and RIGHT$ were
never intended. We left INT(X)
out of the list; it is a feature
of the 8K ROM. You can get around
the lack of LEFT$ and RIGHT$ by
using the LEN(X) function. For
LEFT$(A$,N), just use A$(l TO N) .
For RIGHT$ (A$ , N) , use A$ (LEN (A$ ) -
N+l TO LEN(A$)). Replace
MID$ (A$ , N , M) with A$ (M TO N) . - -AZ

Like all ZX80 users, I have
struggled with the imprecision of
the action of the pressure-
sensitive keyboard. Finally I
came up with a solution. I cut a
set of small clear circles out of
a soft plastic sheet, like the top
of a refrigerator food storage
container, using a paper punch. I
then affixed 1 on each key with
double-stick Scotch tape. The
raised circles guide my fingers to
the key centers and direct the
pressure to the contacts. I can
see the letters through the
circles, but for the first time I
can actually touch- type with a
marked increase in speed and
accuracy.

Julian Alexander Jr. ,
Scotch Plains , NJ

I understand the ZX80's video
blanking during program execution
reflects the designer's preference
for speed over continuous display.

Is it possible, via user
software or simple firmware, to
reallocate some of the Z-80A's
speed to support a video display
while running a program? Second,
is there a technically oriented
manual or documentation for the
ZX80 produced by Sinclair or
others that is available here or
in England?

James Janner Jr. , Seattle, WA

Apparently it is possible. Check
our review of Softsync's ZX80
Invasion game in May's SYNTAX.

The author accomplished continuous
video display using machine
language programming, but we
haven't figured out how yet.

Also, check our story on p.l for a
hardware source, MicroAce's add-on
boards for ZX80s and MicroAces.

Try LINSAC's book, The ZX80
Companion , (available from Image
Computer Products , 615 Academy
Dr., Northbrook, IL 60062,
312/564-5060)) as a ZX80-specific
technical information source.
Others may exist, but I haven't
seen them yet. — AZ

Can the basic circuit from
Build Additional RAM (Mar. 81) be
used to build even larger RAM
modules? I would like to build a
32K version, but I need additional
information .

Charles Los inski, Winona, MN

The ZX80/MicroAce can accomodate
up to 48K RAM externally,
according to David Omstein of
Sinclair. The Z80A can address
64K locations, but the ROM uses
16K. If you write to the empty
ROM addresses, you'll get a write
only memory — the computer will
instantly forget what you wrote.

To build 48K, just bus all data
lines together, then expand the
chip select scheme to decode the
extra addresses, depending on what
size of RAM chips you add. — AZ

I built the interface using
the 8212 (Interface to the Real
World, Jan. 81) and find my address
different from the one in the
article (28672-32767). I checked
my address lines going to the
interface and found them to be
correct. Does the MicroAce differ
from the ZX80 in this respect?

According to Bob Swann of CAI,
they may not. As reported in the
story on p.I, CAI had to revamp
their peripherals design to work
with the new 8K ROM. They are
trying to make the Sinclair
printer commands work on their
printer, but they may have to use
different ones. — AZ

Gerald Johnson, Redwood City, CA

Bill Clark, MicroAce technician,
says the only difference between
the 2 ROMs is that data pins 3 & 4
have been swapped. Otherwise, the
2 ROMs are identical and are
software compatible, meaning that
the same software will work on
both. They are not hardware
compatible, however; you can't put
a MicroAce ROM in a ZX80 because
of the switched data lines. So
your addresses should be the same
whether you use a ZX80 or a
MicroAce . — AZ

Here's an improvement to Joe
Chaiet's Bar Graphics program
(Apr. 81) for 2K MicroAces. Change

th6SG llllGS l

130 IF U(Yi<X THEN PRINT CHR$ (
128);

133 IF Y<10 AND T=1 THEN PRINT

W ;

134 IF Y<10 AND T>1 THEN PRINT
CHR$ (128) ;CHR$ (128) ;

135 IF Y=1 0 AND T=1 THEN PRINT
'V' ;

136 IF Y=10 AND T>1 THEN PRINT
CHR$ (128) ;

Lines 175 and 181 need a ; at the
end. Also, DIM(50) need only be
DIM(10) .

R. Bruce Hosken, Space Coast

Microcomputer Club,
Merritt Island, FL

Will the new LLIST, COPY, and
LPRINT statements (on Sinclair's
8K ROM) control CAI Instruments'
peripherals?

Bill Cotham, Winston-Salem, NC

These SYNTAX readers would like to
hear from others in their areas.

If you would like to contact local
ZX80/MicroAce users, send us your
name and address. We'll publish
them when space permits. — AZ
*John M. Morrison, 327 May land
Ave. , Morrestown, NJ, 08057,
609/234-0230.

*Steven K. Stroh, 4316 Avenue R: ,
Galveston, TX, 77550.

*Bob Childress, 399 Fremont St.,
San Francisco, CA, 94105, 415/421-
7845.

*Bob Irwin in Houston, TX, would
like to hear from other ZX80/
MicroAce users interested in
forming a ZX80 special interest
group on CompuServe. Contact Bob
on CompuServe, 70315,123.

MODIFYING HEX MONITOR FOR 4K

Hex Monitor (May 81) stores
ML programs without shielding them
from BASIC. These changes load ML
to reserved space (program p.8).

In 90 LET S=dec val of start
address of hex code.

In 270, change USR(S) to USR
(dec val of start of computation) .

If you encounter error 4,
increase the number following the
equal sign in line 200 (display
line number where Monitor will
clear the screen and continue) .

On 4K ROM machines , USR (argument)
returns the contents of the HL
register pair or the argument if
HL is not altered.

With 8K ROMs , USR (argument)
returns the contents of the BC
register pair. Also, see the
restrictions on page 167 of the
ZX81 8K manual.

12

8K SYNTACTIC SUM

8K ROM PROGRAM CHANGES

To create the 8K version of
Program 2, key in the program from
the Feb. 81 issue. RUN the program
and key in the numbers from this
new decimal listing:

33 125 64 237 91 12 64 221

33 0 0 124 186 32 8 125

187 32 4 221 229 193 201 78

6 0 221 9 35 24 236

When you have typed in the
final number, error 9/5 appears.
Get back to the listing (LIST) and
delete lines 1-5. SAVE the rest
of the program to tape.

If you use more than IK of
RAM, use the table to alter these

instructions and Program 2.
Always POKE 16388,224 first,
regardless of memory size.

MEM

POKE 16389,

M=

USR()

IK

67

1024

17376

2K

71

2048

18400

4K

79

4096

20448

xK

6 7+4 (x- 1)

x*1024

16352+M

To use Syntactic Sum with the
8K ROM and IK RAM, do these steps:

• POKE 16388,224 and POKE 16389,67
(This replaces Program 1)

• NEW

• LOAD the 8K version of program 2
from tape

• Type GOTO 6 (NL) .

• LOAD or key in the BASIC program
to be slimmed.

• PRINT USR(17376)

Syntactic Sum™ Syntax ZX80 Inc.
and The Harvard Group.

4K SYNTACTIC SUM MODIFICATION

Run Syntactic Sum in less
RAM; change line 20, program 1 to:
20 POKE 17153, M- (M/256)*256

BYTES AVAILABLE

To see how many bytes of RAM
your ROM uses up, type NEW
(NL) , then one of these lines :

(4K ROM) PRINT 17408-PEEK(16400)-
PEEK(16401)*256 (we get 947)

(8K ROM) PRINT 17408-PEEK(16412)-
PEEK( 16413) *256 (we get 815)

Our 8K ROM programs published
in January were written on the
original 8K ROM. To run Chart
Your Biorhythms on the 8K ROMs now
available, change these lines:

109 LET L=6

230 LET B=N(2)-N(1)

290 PRINT AT L, 0;B=N (1 ) -N (2) +1 ;

AT L, (SIN (P2*B/23) *W+W+K) ? "P" ; A
T L, (SIN (P2*B/28) *W+W+K) ; "E" ;AT
L, (SIN (P2*B/33) *W+W+K) ; "I" ; AT
L, (W+K) j " : "

These changes also correct typos
in the published version.

MATRIX DRAWING

This 4K ROM program draws
characters on a 13 by 20 matrix.

To operate, type RUN. When the
computer expects input, enter a
number (1- 13) , indicating which
line you want a character on. The
second input (1-20) , designates
the column. The third input is
the character code of the charac-
ter you want at the designated
location. For 8K, change all
POKEs to write to spare memory.

Robert Ryan, Gladstone, OR

1 LET A=19999
6 LET V=0
10 FOR 1*1 TO 13
20 FOR J=1 TO 20
30 IF V>0 THEN GO TO 50
40 POKE A+ (1*20) +J, 128
50 PRINT CHR$ (PEEK (A+ (1*20 )+J)

) ;

60 IF J=20 THEN PRINT " "

70 NEXT J
80 NEXT I
90 INPUT D
100 INPUT B

110 INPUT C

120 POKE A+(D*20)+B,C

130 CLS

131 CLEAR
135 LET V*1

137 LET A=19999
140 GO TO 10
Syntactic Sum*18662,4K

13

PROGRAMMING LANGUAGE TERMINOLOGY

You've read about BASIC,
machine language (ML) and assembly
language programming in SYNTAX.
What are these languages?

BASIC (which stands for
Beginners' All-purpose Symbolic
Instruction Code) is a high-level
language. This means that you do
not communicate directly with the
machine in its native language,
but in a more complicated one
(that is, more complicated to the
computer) . Programs in BASIC go
through a BASIC interpreter, built
into the ROM, to change them into
machine- readable code. BASIC is
an easy language for beginning
programmers because the commands
resemble simple English words.
Programs in BASIC execute more
slowly than those in lower level
languages because they are broken
down into more machine language
commands than BASIC commands you
started with. Every time you hit
(NL) , for example, the BASIC
interpreter converts that single
instruction into 7 ML commands.

Machine language is just
that- -the language the computer
under stands directly. The
computer thinks only in ones and
zeros, so this language consists
solely of binary representations
of commands and data.

Because most of us don't
think in binary, we have assembly
language as a way to write
programs that are easier for both
the computer and us to under-
stand. Assembly language uses
symbols to stand for memory
addresses, commands and data. You
can enter assembled programs your-
self using a program like Hex
Monitor (May 81) or you can run it
through an assembler, a program
that translates assembly language
into machine language that the
computer can read directly.

Unlike BASIC programs, assembly
symbols translate one-to-one into
ML commands.

PEEK, POKE & CHR$ FOR BEGINNERS (4K)

Most of the BASIC commands on
your ZX80/MicroAce are pretty
clear— SAVE, LOAD, GO TO and RUN
do just what they say they do,

PEEK and POKE are a little tougher
to understand, but as you'll see,
they also do just what they say
they do. CHR$ just translates the
computer's character codes into
the characters themselves.

As we found last month, your
computer stores everything in
memory locations, named by unique
addresses. The ZX80 requires an
address to understand a PEEK
command, so all PEEK commands are
of the form: PEEK (address) . This
tells the computer to look in the
specified address. Adding a PRINT
command before PEEK will make it
display what it finds there.

Typing in PRINT PEEK (address)
(NL) as an immediate mode command
(without a line number) so the
machine executes it right away,
gives an answer on the screen that
Is a number from 0 to 255. Your
computer stores characters in 8
bits, or 1 byte, so 255 is the
largest number it can hold in 1
location. These numbers corres-
pond to the character code set
found on pp. 75-78 of the ZX80 4K
manual and pp. 55-56 of the
MicroAce manual. For example, if
the answer is 38, that is the
character representation in the
address you PEEKed. If you are in
a BASIC area, the character stored
at that address is A. If it's a
machine language area, 38 will be
a ML command or data. PEEK looks
to see what's in the computer's
memory at a given address.

To try this out, clear your
computer by typing NEW (NL) and
type 9876 PRINT A*B. PEEK
addresses in the immediate mode in
order starting with the first
address for BASIC programs, 16424.
(Type with no line number : PRINT
PEEK (16 424), then PRINT PEEK
(16425), and so on.) Don't start

14

with the first RAH address, 16384,
because you will see system vari-
ables which won't make any sense
to you. Look up the answers you
get in the character code table.
They will translate to PRINT A*B
because you PEEKed the beginning
of memory where that line resides.
The first 2 bytes, or addresses,
won't translate to the line n umb er
for reasons explained below.

The computer can also trans-
late the character code for you.
The BASIC command CHR$ will change
the code into a character accord-
ing to the character code table
when you write it in the form
CHR$ (number) and the number is in
the range 0-255.

Putting these 2 ideas
together, let's write a program to
look into memory and tell us what
character, token or keyword is
there. Set up a FOR- NEXT loop to
increment from the starting
address as many as you would like
to see (10 in the example below) .
Then use the CHR$ command to
change the PEEKed code into
characters and keywords :

10 FOR 1=0 TO 10
20 LET S=PEEK(16424+I)

30 PRINT 16424+1, S,CHR$(S)

40 NEXT I

Line 30 prints each address,
character code and code trans-
lation. The commas separate the
answers into columns for easy
reading. You'll see code where
line numbers should be, but they
won't form the line numbers . This
is because the ZX80 stores line
numbers as pure binary code, not
as character codes. When it tries
to translate the binary, it comes
up with garbage using CHR$. To
translate them yourself, multiply
the first byte's code by 256 and
add the second. In our program,
the first 2 codes are 0 and 10,
and (0x256)+10=10, or our first
line number. Change all the line
numbers to 1000s (1000, 2000,
etc.) and the first 2 codes are 3
and 232. (3x256)+232=1000. Try

this for different line numbers,

POKE, on the other hand, puts
something into an address. POKE
commands are of the form: POKE
address , number. The address is
where you want the computer to put
the number after the comma. This
number should also be in the range
0-255 to represent character code
or machine language code.

To our original PEEK program,
now add:

50 POKE 16426,10

60 PRINT PEEK(16426) , CHR$ (PEEK(
16426))

The computer prints the same
information as before. Line 50
puts a new character code into the
first address of the program after
the line number (all line numbers
use up 2 addresses) . Line 60
prints what the computer now finds
at that address and what character
that code translates into. When
you go back to the program list-
ing, you'll see that the transla-
tion for 10 (a graphics character)
has replaced the first word, FOR,
of our first BASIC statement
because you put that value into
that location. This trick can put
characters unavailable from the
keyboard into a program. Our Big
Characters program (Dec. 80) used
this fact to insert the graphics
characters to form the big letters
(some of which aren' t available
from the keyboard) into the
program in a specific order. To
do this yourself, you need to know
the first location of the charac-
ters you want to insert and begin
poking new codes from there on.

POKE commands also allow you
to enter machine language codes
from BASIC into consecutive memory
locations. Because your computer
only understands ML commands and
data in context, poking a value
into a single byte will probably
not get you anywhere. Poking a
series of values can form a
program, as we saw in our analysis
of Sinclair's available memory
program (May 81) .

CLASSIFIEDS

Got something to sell or swap? Or
are you looking for something
special? Use SYNTAX classifieds.
Reach hundreds of other readers
for just $2.75 per line (4 line
min.). Send your ad, typed 35
characters per line, with payment
by 15th of any month for next
month's issue to Classified Ads,
SYNTAX, RD 2 Box 457 Bolton Rd. ,
Harvard, MA 01451.

Programs -games & utility, also
tech data, mods, plans, info, etc.
Send SASE for free goodies list
P.0. Box 3073 San Jose, CA 95116

Handy Utility Programs
S 002 — renumbers BASIC programs,
including GO TO / GO SUB.

S 004 — formatted core dump, with
addr, code, hex, graphics.

S 005 — load, display, correct

machine language programs.
Written in BASIC. $1.00 each or 3
for $2.50. Martin Irons, 46 Magic
Circle Drive, Goshen, NY 10924.

Zilog Z80-CPU Z80A-CPU Technical
Manual, $7.50, and Z80-Assembly
Language Programming Manual,
$15.00. Add 5 % for postage and
handling. Send check or credit
card no. to SYNTAX, RD 2 Box 457

Bolton Rd. , Harvard, MA 01451.

Video secrets revealed 1 This 8-
page document explains in detail
how ZX80 video works, including a
USR routine to run the display.
Also included are an explanation
and USR routine to run the
keyboard and some notes on ROM
routines. $4.00 postpaid. Jim
Williams, 262 Chappel, Calumet
City, IL, 60409.

Nov/Dec SYNTAX combined reprints,
$5, some other back issues avail-
able, $4 each. Send check credit
card no. to SYNTAX, RD 2 Box 457
Bolton Rd. , Harvard, MA, 01451.

For many new ZX80 owners,
this is your first and only
computer. You look to us to help
you understand what to do with it.

To help you, we'd like you to
help us. We're looking for some
beginners to review our beginners'
articles each month. Send vis your
name and address and we'll send
you a copy of each beginners'
story and a self-addressed stamped
envelope. Just read the stories
and tell us what does or doesn't
help you. No payment, no glory,
just better beginners' columns to
help you use your computer better.
Thanks .

THE

H\RV\RD

GROLP

Dolton Road, Harvard, Mass. 01451

First Class

UJ